Systems for monitoring electrical poly-phase equipment for phase-to-phase unbalance, reverse phase sequencing and variations in line voltage are known in the art.
It is known that unbalance of a three-phase power system will occur when single phase loads are applied or coupled to the system, causing one or two of the lines to carry more or less of the load. Excessive phase voltage unbalance causes three-phase motors to run at temperatures above their designated ratings. These high temperatures result in insulation breakdown and shortened motor life.
Three phase motors are designed to rotate clockwise for positive phase sequence and counterclockwise for negative phase sequence. Often only one direction of rotation of the motor is desired and reverse rotation of the motor may cause damage to the equipment designed only to run in one direction.
Operation of three-phase motors at a voltage less than the rated voltage results in higher load current. Since the heat generated due to resistance losses in the motor windings increases proportionately to the current squared (the I.sup.2 R losses), insulation breakdown and shortened motor life may occur.